JP2009032966A - Semiconductor light emitting device - Google Patents

Abstract

A GaN semiconductor layer having a nonpolar plane or a semipolar plane as a principal plane is used, and a stacking fault is intentionally provided in a p-type layer, thereby forming a high hole concentration and extracting light in a favorable polarization state. And a semiconductor laser diode capable of increasing the laser oscillation efficiency and reducing the threshold current.
A semiconductor light emitting device having a stacked structure made of a compound semiconductor (100 to 108) having a crystal growth as a principal plane of crystal growth with a nonpolar plane or semipolar plane other than the c plane. By providing the p-type semiconductor layer 108 that generates the stacking fault I, the crystal growth layer stacked after the p-type semiconductor layer 108 has more crystal defects than the lower portion of the p-type semiconductor layer 108. A semiconductor light emitting device characterized by the above.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a light emitting diode and a semiconductor laser diode having a semiconductor multilayer structure made of a group III nitride semiconductor.

The group III nitride semiconductor is a semiconductor using nitrogen as a group V element in a group III-V semiconductor. Typical examples include aluminum nitride (AlN), gallium nitride (GaN), and indium nitride ((InN). Generally, Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1,0) ≦ x + y ≦ 1), which is referred to as “indium nitride semiconductor” or “GaN semiconductor”.

A nitride semiconductor manufacturing method is known in which a group III nitride semiconductor is grown on a gallium nitride (GaN) substrate having a c-plane as a main surface by metal-organic chemical vapor deposition (MOCVD). ing. By applying this method, a GaN semiconductor multilayer structure having an n-type layer and a p-type layer can be formed, and a light-emitting device using this multilayer structure can be manufactured. Such a light emitting device can be used as a light source of a backlight for a liquid crystal panel, for example.

  The main surface of the GaN semiconductor regrowth on the GaN substrate having the c-plane as the main surface is the c-plane. The light extracted from the c-plane is in a randomly polarized (non-polarized) state. Therefore, when incident on the liquid crystal panel, other than the specific polarized light corresponding to the incident side polarizing plate is shielded and does not contribute to the luminance toward the emission side. Therefore, there is a problem that it is difficult to realize a display with high luminance (efficiency is 50% at the maximum).

  In order to solve this problem, a GaN semiconductor having a main surface other than the c-plane, that is, a non-polar (non-polar) surface such as a-plane or m-plane, or a semi-polar (semi-polar) surface is grown. Fabrication is under consideration. When a light-emitting device having a p-type layer and an n-type layer is manufactured using a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface, light having a strong polarization state can be emitted. Therefore, the loss in the incident side polarizing plate can be reduced by matching the polarization direction of such a light emitting device with the direction of the passing polarized light of the incident side polarizing plate of the liquid crystal panel. As a result, a display with high luminance can be realized.

  On the other hand, short-wavelength laser light sources such as blue and green have come to be used in fields such as high-density recording on optical disks typified by DVD, image processing, medical equipment, and measuring equipment. Such a short wavelength laser light source is composed of, for example, a laser diode using a GaN semiconductor.

A GaN semiconductor laser diode is manufactured by growing a group III nitride semiconductor by a MOCVD method on a gallium nitride (GaN) substrate having a c-plane as a main surface. More specifically, an n-type GaN contact layer, an n-type AlGaN cladding layer, an n-type GaN guide layer, an active layer (light emitting layer), a p-type GaN guide layer, and a p-type AlGaN cladding are formed on the GaN substrate by MOCVD. Then, a p-type GaN contact layer and a p-type GaN contact layer are grown in this order to form a semiconductor stacked structure composed of these semiconductor layers. In the active layer, light emission is caused by recombination of electrons injected from the n-type layer and holes injected from the p-type layer. The light is confined between the n-type AlGaN cladding layer and the p-type AlGaN cladding layer and propagates in a direction perpendicular to the stacking direction of the semiconductor stacked structure. Resonator end faces are formed at both ends in the propagation direction. Light is resonantly amplified while repeating stimulated emission between the pair of resonator end faces, and part of the light is emitted from the resonator end faces as laser light.
T. Takeuchi, et al., “Japanese Journal of Applied Physics, Volume 39 (Jap. J. Appl. Phys. 39)”, 2000, pp. 413-416. A. Chakraborty, et al., “Japanese Journal of Applied Physics, Volume 44 (Jap. J. Appl. Phys. 44)”, 2005, L173

  On the other hand, in the light emitting diode, a technique for scattering light by using the light extraction side surface of the semiconductor layer and the surface of the electrode on the light extraction side as a rough surface (sludge surface) has been conventionally used.

  However, even if polarized light is generated using a GaN semiconductor layer having a nonpolar or semipolar surface as a main surface, if the light extraction side surface of the GaN semiconductor layer or the electrode surface on the light extraction side is rough, Polarization is disturbed by the rough surface. Therefore, when applied to a liquid crystal panel, the loss at the incident-side polarizing plate is increased, and improvement in energy efficiency and display luminance is hindered.

  Of course, the same problem is common not only to light emitting elements using GaN semiconductors but also to light emitting elements using other group III nitride semiconductors.

In a conventional light emitting diode formed using a GaN semiconductor layer having a nonpolar surface or semipolar surface as a main surface, the p-type layer has a low hole concentration and a high resistance. There is a problem that it decreases.

Accordingly, an object of the present invention is to use a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface and intentionally provide a stacking fault in the p-type layer, thereby forming a high hole concentration, low resistance, A semiconductor light emitting device (light emitting diode) using a group III nitride semiconductor with high luminous efficiency is provided.

  One important characteristic of a semiconductor laser diode is a threshold current (oscillation threshold) for causing laser oscillation. The lower this threshold current, the more energy efficient laser oscillation is possible.

  However, since the light generated from the light emitting layer grown with the c-plane as the main surface is randomly polarized, the proportion of light contributing to TE mode oscillation is small. Therefore, the laser oscillation efficiency is not always good, and there is room for improvement in reducing the threshold current.

In addition, a conventional semiconductor laser diode formed using a GaN semiconductor layer having a nonpolar or semipolar surface as a main surface has a problem that the hole concentration of the p-type layer is low and the resistance is high.

  Therefore, an object of the present invention is to use a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface and intentionally provide a stacking fault in the p-type layer, thereby forming a high hole concentration and reducing the resistance. Thus, it is to provide a semiconductor light emitting device (semiconductor laser diode) capable of increasing the light emission efficiency and reducing the threshold current.

According to one embodiment of the present invention for achieving the above object, there is provided a semiconductor light emitting device having a stacked structure made of a compound semiconductor having a nonpolar plane or a semipolar plane as a main surface for crystal growth, By providing a crystal defect layer that generates crystal defects in one, a semiconductor light emitting device is provided in which the upper portion of the crystal defect layer has more crystal defects than the lower portion of the crystal defect layer. .

According to the semiconductor light emitting device (light emitting diode) of the present invention, the hole concentration is increased by using a GaN semiconductor layer having a nonpolar or semipolar surface as a main surface and intentionally providing a stacking fault in the p-type layer. It is possible to provide a semiconductor light emitting device (light emitting diode) using a group III nitride semiconductor that is formed and has low resistance and high efficiency.

According to the semiconductor light emitting device (semiconductor laser diode) of the present invention, by using a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface and intentionally providing a stacking fault in the p-type layer, the hole concentration is reduced. By forming it high and making it low resistance, the light emission efficiency can be increased and the threshold current can be reduced.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention. The technical idea of the present invention is the arrangement of each component as described below. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.

[First embodiment]
FIG. 1 shows a schematic cross-sectional structure of a semiconductor light emitting device according to a first embodiment of the present invention.

The semiconductor light-emitting device according to the first embodiment of the present invention is a semiconductor light-emitting device having a stacked structure made of a compound semiconductor having a plane orientation of a nonpolar plane or a semipolar plane as a main surface for crystal growth.
By providing a crystal defect layer including crystal defects in one of the stacked structures, the crystal growth layer stacked after the crystal defect layer has more crystal defects than the lower part of the crystal defect layer. .

The crystal defect is a stacking fault I.

The compound semiconductor is a semiconductor whose crystal is a hexagonal crystal.

The compound semiconductor may be a group III nitride semiconductor or an oxide semiconductor containing Zn.

Further, the main surface of the laminated structure is a nonpolar surface composed of an m-plane or a-plane.

Further, the growth temperature of the crystal defect layer is different from the growth temperature for growing the crystal growth layers before and after the crystal defect layer. As a result, the stacking fault I can be effectively introduced into the crystal defect layer.

The crystal defect layer is characterized in that the composition is different from the crystal growth layers before and after the crystal defect layer. Also by this, the stacking fault I can be effectively introduced into the crystal defect layer.

In addition, a p-type semiconductor layer is provided above the crystal defect layer.

In addition, the crystal defect layer is present in or on an active layer that generates light, and further has a p-type semiconductor layer on the crystal defect layer.

  As shown in FIG. 1, the semiconductor light emitting device according to the first embodiment of the present invention includes an n-type semiconductor layer 100, an active layer 102 disposed on the n-type semiconductor layer 100, and an active layer 102. The p-type semiconductor layer 104 disposed above, the AlGaN barrier layer 106 disposed on the p-type semiconductor layer 104, and the p-type semiconductor layer 108 disposed on the AlGaN barrier layer 106 and introducing the stacking fault I. With.

By intentionally providing the stacking fault I in the p-type semiconductor layer 108, the acceptor impurity density NA in the p-type semiconductor layer 108 can be increased, and the carrier density of holes in the p-type semiconductor layer 108 is increased. Can be high.

FIG. 2 is a schematic diagram for explaining a nonpolar plane and a semipolar plane. FIG. 2A is a schematic diagram showing a crystal structure of a group III nitride semiconductor, and FIG. 2B and FIG. (C) is a schematic diagram for explaining the semipolar plane, and FIG. 2 (d) is a schematic diagram showing a bond between a group III atom and a nitrogen atom.

As shown in FIGS. 2A and 2D, the crystal structure of the group III nitride semiconductor can be approximated by a hexagonal system, and four nitride atoms are bonded to one group III atom. Yes. Four nitrogen atoms are located at four vertices of a regular tetrahedron having a group III atom arranged at the center. Of these four nitrogen atoms, one nitrogen atom is positioned in the + c axis direction with respect to the group III atom, and the other three nitrogen atoms are positioned on the −c axis side with respect to the group III atom. Because of such a structure, the polarization direction is along the c-axis in the group III nitride semiconductor.

  The c-axis is along the axial direction of the hexagonal column, and the plane (the top surface of the hexagonal column) having the c-axis as a normal is the c-plane {0001}. When the group III nitride semiconductor crystal is cleaved by two planes parallel to the c plane, the + c axis side plane (+ c plane) becomes a crystal plane in which group III atoms are arranged, and the −c axis side plane (−c plane) ) Is a crystal plane with nitrogen atoms. For this reason, the c-plane is called a polar plane because it exhibits different properties on the + c-axis side and the −c-axis side.

  Since the + c plane and the −c plane are different crystal planes, different physical properties are exhibited accordingly. Specifically, it is known that the + c surface has high durability against chemical reactions such as resistance to alkali, and conversely, the −c surface is chemically weak and is soluble in alkali, for example.

  On the other hand, the side surfaces of the hexagonal columns are m-planes {10-10}, respectively, and the planes passing through a pair of ridge lines that are not adjacent to each other are a-planes {11-20}. Since these are crystal planes perpendicular to the c-plane and orthogonal to the polarization direction, they are nonpolar planes, that is, nonpolar planes. Furthermore, as shown in FIGS. 2B and 2C, crystal planes {10-11} and {10-13} that are inclined with respect to the c-plane (not parallel nor perpendicular) are Since it crosses diagonally with respect to the polarization direction, it is a plane with some polarity, that is, a semipolar plane. Specific examples of other semipolar planes are planes such as {10-1-1} plane, {10-1-3} plane, {11-22} plane.

For example, a GaN single crystal substrate having an m-plane as a main surface can be produced by cutting from a GaN single crystal having a c-plane as a main surface. The m-plane of the cut substrate is polished by, for example, a chemical mechanical polishing process, and the orientation error with respect to both the [0001] direction and the [11-20] direction is within ± 1 ° (preferably ± 0.3 °). Within). In this way, a GaN single crystal substrate having an m-plane as a main surface is obtained.

A light emitting diode (LED) and semiconductor laser diode (LD) structure is formed on the GaN single crystal substrate thus obtained by MOCVD.

3 to 5 are diagrams based on results published in Journal of Applied Physics, 94 (6), 2003 by Vurgaftman and Mayer.

FIG. 3 is a schematic explanatory view of the crystal structure of the semiconductor light emitting device according to the first embodiment of the present invention. In a hexagonal crystal such as gallium nitride, when crystal growth is performed in the [0001] c-axis direction, stacking faults are formed in a plane parallel to the c-plane, and the stacking faults behave in the same manner as the cubic Z.

That is, a relationship of P _{sp, ZB} ≠ P _{sp, wurtzite} holds between the spontaneous polarization P _{sp, ZB} of the cubic crystal and the spontaneous polarization P _{sp, wurtzite} of the hexagonal crystal. As a result, the cubic Z and the hexagonal W In this heterojunction, a stacking fault corresponding to cubic Z is introduced. In the hexagonal (ABCABC ...) gallium nitride, the stacking fault portion is equivalent to the presence of a cubic crystal (ABABA ...), and the heterojunction of the cubic Z and hexagonal W is (ABCABBC.・ ・)

For this reason, by introducing stacking faults, superlattice structures having different band gaps are formed. If there is a stacking fault in the active layer, the light emission efficiency is lowered, but if there is a stacking fault only in the p-type layer, both high light emission efficiency and low p-type layer resistance can be achieved.

FIG. 4 is a schematic explanatory view of the crystal structure of the semiconductor light emitting device according to the first embodiment of the present invention, and is a stacking fault layer (cubic) sandwiched between hexagonal crystals (wurtzite crystal structure: wurtzite). The relationship between the distance (angstrom) in the [0001] direction of crystal Z: zincblende) and the energy band is shown. FIG. 4 shows a non-doped crystal, and a Fermi level Ef exists near the approximate center of the conduction band CB and the valence band VB. A stacking fault corresponding to the cubic crystal Z exists in a portion sandwiched between the hexagonal crystals W.

FIG. 5 is a schematic explanatory view of the crystal structure of the semiconductor light emitting device according to the first embodiment of the present invention. In the case where the acceptor impurity density is 1 × 10 ¹⁸ cm ⁻³ , The relationship between the distance (angstrom) in the [0001] direction of the stacking fault layer (cubic Z: zincblende) sandwiched between the wurtzite crystal structure W (wurtzite) and the energy band is shown. When the acceptor impurity density is 1 × 10 ¹⁸ cm ⁻³ , the acceptor impurity density level is surely increased by the stacking fault represented by the cubic Z sandwiched between the hexagonal crystals W, and the desired high impurity density is obtained. It can be seen that impurity addition can be performed.

FIG. 6 is a schematic explanatory view of a stacking fault in the cross-sectional structure of the semiconductor light emitting device according to the first embodiment of the present invention, and FIG. FIG. 6B is a diagram illustrating a state in which (p-type semiconductor layers 108 and 109) are continuously formed, and FIG. 6B illustrates a state in which stacking faults are formed in the m-axis direction perpendicular to the m-plane. FIG. 6C is a diagram illustrating a state in which stacking faults are formed in a direction parallel to the c-plane (m-axis direction perpendicular to the m-plane).

According to the semiconductor light emitting element (light emitting diode) according to the first embodiment of the present invention, a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface is used, and a stacking fault is intentionally formed in the p-type layer. By providing, it is possible to form a high hole concentration and extract light in a favorable polarization state.

According to the semiconductor light emitting device (semiconductor laser diode) according to the first embodiment of the present invention, a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface is used, and a p-type layer (p-type semiconductor layer 108) is used. 109) by intentionally providing the stacking fault I, the hole concentration can be increased, the laser oscillation efficiency can be increased, and the threshold current can be reduced.

[Second Embodiment]
FIG. 7 is a schematic sectional view of a semiconductor light emitting device according to the second embodiment of the present invention.

  A semiconductor light-emitting device according to a second embodiment of the present invention is a semiconductor light-emitting device having a stacked structure made of a compound semiconductor having a nonpolar plane or a semipolar plane as a main surface for crystal growth, and at least an n-type layer And a group III nitride semiconductor layer having a stacked structure having a p-type layer, the light extraction side surface of the group III nitride semiconductor layer is a mirror surface, and a crystal that generates stacking fault I in one of the stacked structures By providing the defect layer, the crystal growth layer laminated after the crystal defect layer has more crystal defects than the lower part of the crystal defect layer.

  In addition, a transparent electrode in contact with the light extraction side surface of the group III nitride semiconductor layer is further provided, and the light extraction side surface of the transparent electrode is a mirror surface.

Further, the transparent electrode is characterized by comprising a transition metal film having a thickness of 200 angstroms (angstrom) or less.

The transparent electrode is made of a metal oxide film.

Further, the unevenness of the light extraction side surface of the transparent electrode is not more than λ / n1 (where n1 is the refractive index of the transparent electrode) with respect to the emission wavelength λ.

Further, the unevenness of the light extraction side surface of the group III nitride semiconductor layer is not more than λ / n2 (where n2 is the refractive index of the group III nitride semiconductor layer) with respect to the emission wavelength λ.

In addition, the semiconductor light emitting device according to the second embodiment of the present invention has a laminated structure made of a compound semiconductor having a crystal growth as a principal plane of crystal growth with a plane orientation of a nonpolar plane or a semipolar plane other than the c plane. An element comprising a group III nitride semiconductor layer having a laminated structure having at least an n-type layer and a p-type layer, an electrode provided on the surface of the group III nitride semiconductor layer, and one of the laminated structures By providing the crystal defect layer that generates the stacking fault I, the crystal growth layer stacked after the crystal defect layer has more crystal defects than the lower portion of the crystal defect layer.

The electrode is a p-side electrode.

Further, the light output of the light emitting layer from the nonpolar plane or the semipolar plane is characterized in that the light output in the c-axis direction is five times or more than the light output in the a-axis direction.

As shown in FIG. 7, the light-emitting diode according to the second embodiment of the present invention is configured by re-growing a group III nitride semiconductor layer 2 on a GaN (gallium nitride) single crystal substrate 1.
The group III nitride semiconductor layer 2 includes an n-type contact layer 21, a quantum well (QW) as a light emitting layer, a GaN final barrier layer 25, a p-type electron blocking layer 23, in order from the GaN single crystal substrate 1 side. And a p-type contact layer 24 is laminated.

An anode electrode 3 as a transparent electrode is formed on the surface of the p-type contact layer 24, and a connection portion 4 for wiring connection is joined to a part of the anode electrode 3. The cathode electrode 5 is bonded to the n-type contact layer 21. Thus, a light emitting diode structure is formed.

As shown in FIG. 7, the stacking fault I is introduced into the p-type contact layer 24, and the impurity addition amount of, for example, magnesium (Mg), which is an acceptor impurity, is substantially increased. As a result, the carrier density of holes can be increased.

In addition, the p-type contact layer 24 may be formed not only as a single layer structure but also as a two-layer to four-layer structure. In that case, the stacking fault I introduced into each layer is below the crystal defect layer. In comparison, there are more crystal growth layers stacked after the crystal defect layer.

Alternatively, in the p-type contact layer 24 having a multilayer structure, the introduction density of the stacking fault I can be changed to change the carrier density of holes in each layer.

  The GaN single crystal substrate 1 is bonded to a support substrate (wiring substrate) 10. Wirings 11 and 12 are formed on the surface of the support substrate 10. The connecting portion 4 and the wiring 11 are connected by a bonding wire 130, and the cathode electrode 5 and the wiring 12 are connected by a bonding wire 140. Further, although not shown in the drawings, the light emitting diode element is configured by sealing the light emitting diode structure and the bonding wires 130 and 140 with a transparent resin such as an epoxy resin.

The n-type contact layer 21 is composed of an n-type GaN layer to which silicon is added as an n-type dopant. The layer thickness is preferably 3 μm or more. The doping concentration of silicon is, for example, about 10 ¹⁸ cm ⁻³ .

  The quantum well is formed by alternately laminating a silicon-doped InGaN layer (for example, about 3 nm thickness) and a GaN layer (for example, about 9 nm thickness) for a predetermined period (for example, five periods). A GaN final barrier layer 25 (for example, about 40 nm thick) is laminated between this quantum well and the p-type electron blocking layer 23.

The p-type electron blocking layer 23 is composed of an AlGaN layer to which magnesium as a p-type dopant is added. The layer thickness is, for example, about 28 nm. The doping concentration of magnesium is, for example, about 3 × 10 ¹⁹ cm −3.

The p-type contact layer 24 is composed of a GaN layer to which magnesium as a p-type dopant is added at a high concentration. The layer thickness is, for example, about 70 nm. The doping concentration of magnesium is, for example, about 10 ²⁰ cm ⁻³ . The surface of the p-type contact layer 24 forms the surface 2a of the group III nitride semiconductor layer 2, and this surface 2a is a mirror surface.

More specifically, the unevenness of the surface 2a is about 100 nm or less. If the refractive index of GaN is n2 (n2≈2.5) and the emission wavelength is λ, if the unevenness of the surface 2a is less than or equal to λ / n2, the unevenness can substantially affect the light. It can be said that there is no mirror surface. The surface 2a is a light extraction side surface from which light generated in the quantum well is extracted.

  The anode electrode 3 is composed of a transparent thin metal layer (for example, about 200 mm or less) composed of Ni and Au. Since the surface 2a of the group III nitride semiconductor layer 2 is a mirror surface, the surface 3a (light extraction side surface) of the anode electrode 3 formed in contact with the surface 2a is also a mirror surface. That is, the unevenness of the surface 3a is, for example, about 100 nm or less. When the refractive index n1 of the anode electrode 3 (n1 is 1.6 to) and the emission wavelength is λ, if the unevenness of the surface 3a is not more than λ / n1, the unevenness substantially affects the light. It can be said that it is a mirror surface without any problems.

Thus, since the light extraction side surface 2a of the group III nitride semiconductor layer 2 and the light extraction side surface 3a of the anode electrode 3 are both mirror surfaces, the light generated from the quantum well has little influence on the polarization state. It will be taken out to the anode electrode 3 side without giving.

  The cathode electrode 5 is a film composed of Ti and an Al layer.

  The GaN single crystal substrate 1 is a substrate made of a GaN single crystal having a main surface other than the c-plane. More specifically, the main surface is a nonpolar surface or a semipolar surface. More specifically, the main surface of the GaN single crystal substrate 1 is a surface having an off angle within ± 1 ° from the plane orientation of the nonpolar plane, or within ± 1 ° from both positions of the semipolar plane. A surface having an off angle.

The peak wavelength at the drive current of 20 mA is, for example, about 435 nm (blue region). The peak wavelength at a driving current of 1 mA is, for example, about 437 nm, and the peak wavelength at a driving current of 100 mA is 434 nm. That is, the fluctuation of the peak wavelength due to the drive current is about 3 nm, for example. Since the unevenness of the surface 2a of the group III nitride semiconductor layer 2 and the surface 3a of the anode electrode 3 is, for example, about 100 nm or less, it hardly affects the polarization of light in the wavelength region.

  It has also been confirmed that the polarization direction of EL emission is orthogonal to the c-axis (polarization in the a-axis direction), and the polarization ratio is, for example, about 0.77 when the drive current is 1 mA. The polarization ratio is a value given by (Io−Ip) / (Io + Ip) by the polarization intensity Io (polarization intensity in the a-axis direction) orthogonal to the c-axis and the polarization intensity Ip parallel to the c-axis. In general, since light propagates in a direction perpendicular to the direction of polarization, the polarization component in the a-axis direction propagates in the c-axis direction. As a result, the light output in the c-axis direction is at least five times the light output in the a-axis direction.

According to the semiconductor light emitting device (light emitting diode) according to the second embodiment of the present invention, a GaN semiconductor layer whose main surface is a nonpolar surface or a semipolar surface is used, and a p-type layer (p-type contact layer 24). By intentionally providing the stacking fault I, the hole concentration can be increased and light with a good polarization state can be extracted.

[Third embodiment]
FIG. 8 is a perspective view for explaining the structure of a semiconductor light emitting device (semiconductor laser diode) according to the third embodiment of the present invention. 9 shows a longitudinal sectional view taken along line II-II in FIG. 8, and FIG. 10 shows a transverse sectional view taken along line III-III in FIG.

A semiconductor light emitting device (semiconductor laser diode) according to a third embodiment of the present invention is a semiconductor light emitting device having a stacked structure made of a compound semiconductor having an m-plane as a main surface for crystal growth, and in the m-axis direction, A group III nitride semiconductor multilayer structure in which an n-type cladding layer, a light emitting layer, and a p-type cladding layer are stacked, and a crystal defect layer that generates stacking faults is provided in one of the stacked structures, thereby In comparison, the crystal growth layer laminated after the crystal defect layer has more crystal defects.

  Further, the group III nitride semiconductor is characterized in that it is crystal-grown on a GaN single crystal substrate having an m-plane as a regrowth plane for crystal growth.

  In addition, the off-angle of the main surface of the GaN single crystal substrate is within ± 1 °.

  The group III nitride semiconductor multilayer structure includes a p-type semiconductor layer including a p-type cladding layer, and the semiconductor light emitting element is formed along a predetermined direction and is in contact with the p-type semiconductor layer in a striped contact region. A p-side electrode is further provided, and a pair of resonator end faces are formed perpendicular to the stripe direction of the contact region.

  Further, the surface of the p-type semiconductor excluding the stripe contact region is protected by an insulating film.

The group III nitride semiconductor multilayer structure includes a p-type semiconductor layer including a p-type cladding layer, a part of the p-type semiconductor layer is removed, and a stripe along a predetermined direction is formed. A pair of resonator end faces are formed perpendicular to the direction.

Further, the stripe is formed in a ridge shape, and the surface of the stripe except for the contact portion between the stripe and the p-side electrode is protected by an insulating film.

Further, the stripe direction is a c-axis direction, and the pair of resonator end faces are a + c plane and a −c plane.

Further, the resonator end face of the −c plane is covered with a protective film made of an insulating film.

Further, the light-emitting layer has a quantum well structure, and the flatness in the c-axis direction of the quantum well constituting the quantum well structure is 10 mm or less.

The stripe direction is the a-axis direction, and the pair of resonator end faces are a-planes.

Further, the resonator end face is a cleavage plane.

Further, a plurality of contact regions to the p-type semiconductor layer are provided.

A p-side electrode is formed on the m-plane of the p-type semiconductor layer, and the group III nitride semiconductor multilayer structure is grown on one main surface of the conductive substrate. The other main surface of the conductive substrate Is an m-plane, and an n-side electrode is formed on the other main surface.

  The group III nitride semiconductor multilayer structure includes a layer containing In having biaxial stress between the n-type cladding layer and the substrate carrying the group III nitride semiconductor multilayer structure. And

  The light emitting layer has a multiple quantum well structure in which the number of quantum wells containing In is 3 or less, and the group III nitride semiconductor multilayer structure includes a pair of guide layers disposed with the light emitting layer interposed therebetween, The n-type clad layer is a clad layer that includes at least Al having a wider hand gap than the guide layer, and is disposed so as to sandwich one of the pair of guide layers between the light-emitting layer. The other guide layer is disposed between the light emitting layer and a clad layer containing at least Al having a wider hand gap than the guide layer.

  A semiconductor light emitting device (semiconductor laser diode 70) according to a third embodiment of the present invention includes a GaN single crystal substrate 71, a group III nitride semiconductor multilayer structure 72 formed by crystal growth on the GaN single crystal substrate 71, and The n-side electrode 73 formed so as to be in contact with the back surface of the GaN single crystal substrate 1 (the surface opposite to the group III nitride semiconductor multilayer structure 72) and the surface of the group III nitride semiconductor multilayer structure 72 It is a Fabry-Perot type provided with the p-side electrode 40 formed as described above.

  The GaN single crystal substrate 71 has an m-plane as a main surface, and a group III nitride semiconductor multilayer structure 72 is formed by crystal growth on the main surface. Therefore, the group III nitride semiconductor multilayer structure 72 is made of a group III nitride semiconductor having the m-plane as the crystal growth main surface.

  The group III nitride semiconductor multilayer structure 72 includes a light emitting layer 80, an n-type semiconductor layer 81, and a p-type semiconductor layer 82.

The n-type semiconductor layer 81 is disposed on the GaN single crystal substrate 71 side with respect to the light emitting layer 80, and the p-type semiconductor layer 82 is disposed on the p-side electrode 40 side with respect to the light emitting layer 80. Thus, the light emitting layer 80 is sandwiched between the n-type semiconductor layer 81 and the p-type semiconductor layer 82, and a double heterojunction is formed. Electrons are injected from the n-type semiconductor layer 81 and holes are injected from the p-type semiconductor layer 82 into the light emitting layer 80. When these are recombined in the light emitting layer 80, light is generated.

  The n-type semiconductor layer 81 includes an n-type GaN contact layer 83 (for example, 2 μm thickness), an n-type AlGaN cladding layer 84 (for a thickness of 1.5 μm or less, for example, 1.0 μm thickness), and an n-type in order from the GaN single crystal substrate 71 side. A GaN guide layer 85 (for example, 0.1 μm thick) is laminated.

On the other hand, the p-type semiconductor layer 82 is formed on the light-emitting layer 80 in the order of a p-type AlGaN electron blocking layer 86 (for example, 20 nm thick), a p-type GaN guide layer 87 (for example, 0.1 μm thick), and a p-type AlGaN cladding layer. 88 (1.5 μm thickness or less, for example, 0.4 μm thickness) and a p-type GaN contact layer 89 (for example, 0.3 μm thickness) are laminated.

The n-type GaN contact layer 83 and the p-type GaN contact layer 89 are low resistance layers for making ohmic contact with the n-side electrode 73 and the p-side electrode 40, respectively. The n-type GaN contact layer 83 is made an n-type semiconductor by doping GaN with, for example, Si as an n-type dopant at a high concentration (doping concentration is, for example, 3 × 10 ¹⁸ cm ⁻³ ). The p-type AlGaN contact layer 89 is formed as a p-type semiconductor layer by doping Mg as a p-type dopant at a high concentration (doping concentration is 3 × 10 ¹⁹ cm ⁻³ , for example).

  The n-type AlGaN cladding layer 84 and the p-type AlGaN cladding layer 88 have a light confinement effect that confines light from the light emitting layer 80 therebetween.

The n-type AlGaN cladding layer 84 is made an n-type semiconductor by doping AlGaN with, for example, Si as an n-type dopant (doping concentration is, for example, 1 × 10 ¹⁸ cm ⁻³ ). The p-type AlGaN cladding layer 88 is made into a p-type semiconductor layer by doping Mg as a p-type dopant (doping concentration is, for example, 1 × 10 ¹⁹ cm ⁻³ ). The n-type AlGaN cladding layer 84 has a wider band gap than the n-type GaN guide layer 85, and the p-type AlGaN cladding layer 88 has a wider band gap than the p-type GaN guide layer 87. Thereby, good confinement can be performed, and a low threshold and high efficiency semiconductor laser diode can be realized.

As shown in FIG. 8, the stacking fault I is introduced into the p-type AlGaN cladding layer 88 and the p-type GaN contact layer 89, and an impurity addition amount of, for example, magnesium (Mg), which is substantially an acceptor impurity, is increased. It is increasing. As a result, the carrier density of holes can be increased.

In addition, the p-type AlGaN cladding layer 88 may be formed not only as a single layer structure but also as a two-layer to four-layer structure. In that case, the stacking fault I introduced into each layer is below the crystal defect layer. Compared to the above, there are more crystal growth layers stacked after the crystal defect layer.

Alternatively, in the p-type AlGaN cladding layer 88 having a multilayer structure, the introduction density of the stacking fault I can be changed to change the hole carrier density of each layer.

The n-type GaN guide layer 85 and the n-type GaN guide layer 87 are semiconductor layers that generate a carrier confinement effect for confining carriers (electrons and holes) in the light emitting layer 80. Thereby, the efficiency of recombination of electrons and holes in the light emitting layer 80 is increased. The n-type GaN guide layer 85 is an n-type semiconductor by doping GaN with, for example, Si as an n-type dopant (doping concentration is, for example, 1 × 10 ¹⁸ cm ⁻³ ). The layer 87 is made a p-type semiconductor by doping GaN with, for example, Mg as a p-type dopant (doping concentration is, for example, 5 × 10 ¹⁸ cm ⁻³ ).

The p-type AlGaN electron block layer 86 is a p-type semiconductor formed by doping AlGaN with, for example, Mg as a p-type dopant (doping concentration is, for example, 5 × 10 ¹⁸ cm ⁻³ ). This prevents the outflow of electrons from the substrate and increases the recombination efficiency of electrons and holes.

  The light emitting layer 80 has, for example, an MQW structure containing InGaN, and is a layer for generating light by recombination of electrons and holes and amplifying the generated light. Specifically, the light emitting layer 80 is configured by alternately laminating an InGaN layer (for example, 3 nm thickness) and a GaN layer (for example, 9 nm thickness) alternately for a plurality of periods. In this case, since the InGaN layer has an In composition ratio of 5% or more, the band gap becomes relatively small, and a quantum well layer is formed. On the other hand, the GaN layer functions as a barrier layer (barrier layer) having a relatively large band gap. For example, the InGaN layer and the GaN layer are alternately and repeatedly stacked for 2 to 7 periods to form the light emitting layer 80 having the MQW structure. The emission wavelength is set to 400 nm to 550 nm by adjusting the composition of In in the quantum well layer (InGaN layer). In the MQW structure, the number of quantum wells containing In is preferably 3 or less.

  The p-type semiconductor layer 82 is partially removed to form the ridge stripe 20. More specifically, a part of the p-type contact layer 89, the p-type AlGaN cladding layer 88, and the p-type GaN guide layer 87 are removed by etching to form a ridge stripe 20 having a substantially trapezoidal shape (mesa shape) in cross section. ing. The ridge stripe 20 is formed along the c-axis direction.

  The group III nitride semiconductor multilayer structure 72 has a pair of resonator end faces 91 and 92 (cleavage planes) formed by cleavage at both longitudinal ends of the ridge stripe 20. The pair of resonator end faces 91 and 92 are parallel to each other, and both are perpendicular to the c-axis. Thus, the n-type GaN guide layer 85, the light emitting layer 80, and the p-type GaN guide layer 87 form a Fabry-Perot resonator having the resonator end surfaces 91 and 92 as the resonator end surfaces.

That is, the light generated in the light emitting layer 80 is amplified by stimulated emission while reciprocating between the resonator end faces 91 and 92. A part of the amplified light is extracted from the resonator end faces 91 and 92 as laser light to the outside of the element.

The n-side electrode 73 is made of, for example, Al metal, and the p-side electrode 40 is made of, for example, Al metal or a Pd / Au alloy, and is ohmically connected to the p-type contact layer 89 and the GaN single crystal substrate 71, respectively. The exposed surfaces of the n-type GaN guide layer 87 and the p-type AlGaN cladding layer 88 are covered so that the p-side electrode 40 contacts only the p-type GaN contact layer 89 on the top surface (stripe-shaped contact region) of the ridge stripe 20. An insulating layer 76 is provided. As a result, the current can be concentrated on the ridge stripe 20, so that efficient laser oscillation is possible. Further, since the surface of the ridge stripe 20 except the contact portion with the p-side electrode 40 is covered and protected by the insulating layer 76, the lateral light confinement can be moderated to facilitate the control. In addition, leakage current from the side surface can be prevented. The insulating layer 76 can be made of an insulating material having a refractive index larger than 1, for example, SiO ₂ or ZrO ₂ .

  Further, the top surface of the ridge stripe 20 is an m-plane, and a p-side electrode 40 is formed on the m-plane. The back surface of the GaN single crystal substrate 71 on which the n-side electrode 73 is formed is also m-plane. As described above, since both the p-side electrode 40 and the n-side electrode 73 are formed on the m-plane, it is possible to realize reliability that can sufficiently withstand high-power laser and high-temperature operation.

  The resonator end faces 91 and 92 are covered with insulating films 93 and 94 (not shown in FIG. 8), respectively. The resonator end surface 91 is a + c-axis side resonator end surface, and the resonator end surface 92 is a −c-axis side resonator end surface. That is, the crystal face of the resonator end face 91 is a + c plane, and the crystal face of the resonator end face 92 is a −c plane. The insulating film 94 on the −c plane side can function as a protective film that protects the chemically weak −c plane such as being dissolved in alkali, and contributes to improving the reliability of the semiconductor laser diode 70.

According to the semiconductor light emitting device (semiconductor laser diode) according to the third embodiment of the present invention, a GaN semiconductor layer having a nonpolar plane or a semipolar plane as a main surface is used, and a p-type layer (p-type AlGaN cladding layer) is used. 88 and the p-type GaN contact layer 89) are intentionally provided with the stacking fault I, whereby the hole concentration can be increased, the laser oscillation efficiency can be increased, and the threshold current can be reduced.

[Other embodiments]
As mentioned above, although 1st thru | or 3rd embodiment was demonstrated this invention, the description and drawing which make a part of this indication do not limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

As described above, the present invention has been described according to the first to third embodiments, but it is needless to say that the present invention includes various embodiments that are not described herein. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

1 is a schematic cross-sectional structure diagram of a semiconductor light emitting element according to a first embodiment of the present invention. It is a schematic diagram for demonstrating a nonpolar surface and a semipolar surface, Comprising: (a) The schematic diagram which shows the crystal structure of a group III nitride semiconductor, (b) For describing the semipolar surface {10-11} Schematic diagram, c) Schematic diagram for explaining the semipolar plane {10-13}, (d) Schematic diagram showing the bond between group III atoms and nitrogen atoms. 1 is a schematic explanatory view of a crystal structure of a semiconductor light emitting element according to a first embodiment of the present invention. It is a typical explanatory view of the crystal structure of the semiconductor light emitting device according to the first embodiment of the present invention, and a stacking fault layer (cubic Z: zincblende) sandwiched between hexagonal crystals (wurtzite crystal structure W: wurtzite) FIG. 5 is a diagram showing the relationship between the distance (angstrom) in the [0001] direction and the energy band. FIG. 3 is a schematic explanatory view of the crystal structure of the semiconductor light emitting device according to the first embodiment of the present invention, in the case where the acceptor impurity density is 1 × 10 ¹⁸ cm ⁻³ , which is a hexagonal crystal (wurtzite crystal structure W: The relationship diagram of the distance (angstrom) in the [0001] direction of the stacking fault layer (cubic Z: zincblende) sandwiched between wurtzite) and the energy band. BRIEF DESCRIPTION OF THE DRAWINGS It is typical explanatory drawing of the stacking fault in the cross-section of the semiconductor light-emitting device concerning the 1st Embodiment of this invention, Comprising: (a) The mode that a stacking fault is continuously formed with the multilayer structure of m surface is demonstrated. (B) A diagram illustrating a state in which stacking faults are formed in the m-axis direction perpendicular to the m-plane, (c) stacking faults in a direction parallel to the c-plane (m-axis direction perpendicular to the m-plane). The figure explaining a mode that it forms. The typical cross-section figure of the light emitting diode which concerns on the 2nd Embodiment of this invention. The perspective view for demonstrating the structure of the semiconductor laser diode which concerns on the 3rd Embodiment of this invention. FIG. 9 is a longitudinal sectional view taken along line II-II in FIG. 8. FIG. 9 is a transverse sectional view taken along line III-III in FIG. 8.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... GaN single crystal substrate 2 ... Group III nitride semiconductor layer 2a ... Surface (mirror surface) of GaN semiconductor layer
3 ... Anode electrode (transparent electrode) (n-side electrode)
3a: Anode electrode surface (mirror surface)
4 ... Connection part 5 ... Cathode electrode 7 ... Recess 10 ... Support substrate 11, 12 ... Wiring 83 ... n-type GaN contact layer 84 ... n-type AlGaN cladding layer 85 ... n-type GaN guide layer 86 ... p-type AlGaN electron block layer 87 ... p-type GaN guide layer 88 ... p-type AlGaN cladding layer 89 ... p-type GaN contact layer 21 ... n-type contact layer 20 ... ridge stripe 21a ... surface of n-type contact layer (surface of GaN semiconductor layer: mirror surface)
22 ... Quantum well layer 23 ... p-type electron blocking layer 24 ... p-type contact layer 25 ... final barrier layer 40 ... p-side electrode 70 ... semiconductor laser diode 71 ... substrate (GaN single crystal substrate)
72 ... Group III nitride semiconductor laminated structure 73 ... n-side electrodes 76, 93, 94 ... insulating layers 80, 102 ... light emitting layer (active layer)
81, 100 ... n-type semiconductor layers 82, 104, 108, 109 ... p-type semiconductor layers 91, 92 ... resonator end faces 106 ... AlGaN barrier layers 130, 140 ... bonding wires I ... stacking faults

Claims (9)

  A semiconductor light-emitting device having a stacked structure made of a compound semiconductor having a nonpolar plane or a semipolar plane as a main surface for crystal growth, wherein a crystal defect layer that generates a crystal defect is provided in one of the stacked structures, A semiconductor light emitting device characterized in that the upper part of the crystal defect layer has more crystal defects than the lower part of the crystal defect layer.   The semiconductor light emitting device according to claim 1, wherein the crystal defect is a stacking fault.   The semiconductor light emitting element according to claim 1, wherein the crystal made of the compound semiconductor is a semiconductor made of hexagonal crystal.   4. The semiconductor light emitting device according to claim 1, wherein the crystal made of the compound semiconductor is a group III nitride semiconductor or an oxide semiconductor containing Zn. 5.   5. The semiconductor light emitting element according to claim 1, wherein a main surface of the multilayer structure is a nonpolar surface. 6.   The growth temperature of the crystal defect layer is different from the growth temperature for growing an upper or lower crystal growth layer of the crystal defect layer, according to any one of claims 1 to 5. The semiconductor light emitting element as described.   7. The semiconductor light emitting element according to claim 1, wherein the crystal defect layer has a composition different from that of an upper or lower crystal growth layer of the crystal defect layer.   8. The semiconductor light emitting device according to claim 1, further comprising a p-type layer on the crystal defect layer.   8. The semiconductor according to claim 1, wherein the crystal defect layer is present in an active layer or an upper part thereof, and further has a p-type layer on the crystal defect layer. 9. Light emitting element.

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